PLATE XXVIII 



i. Group illustrating the life-history of Magitus. The young shells 

 attach themselves to growing coral, in which they become embedded, 

 and have to extend the shell as the coral grows, so as to keep the 

 aperture opsn to the sea. 



A, Adult specimen diwded lengthwise, to show the space occupied 



by the animal and the infilled older portion. 



B, Exterior of the same specimen, showing lines of increment and 



counterpart of the young shell. 



C, Exterior of another, more contorted specimen, showing the 



sculpturing of the shell. The notch near the middle was 

 made by some other mollusc, boring into the coral mass. 

 a.c, anterior canal. 



D, Young shells. 



E, Portion of a burrow in the coral. 



F, Mass of coral broken open, to show the shells as they occur 



in situ : m.b., mouths of burrows ; 5., section of Magilus shell. 



2. Cymatium olearium, Linn. : a, with the periostracum on, as in 

 life ; b, the shell as seen after the removal of the periostracum. 



3, a, b. Upper and under view of Xenophora conchyliophora, Born, 

 showing how completely the shell is covered by the debris built on by 

 the animal. (From specimen in the possession of the author.) 



[Groups i and i are reproduced by permission of the Trustees from specimens 

 on exhibition in the Natural History Museum ] 



